Objective: Explore prescribing patterns in overall and by patients’ health schemes between Thai fiscal year 2009 and 2010, and estimate possible saving if this policy was extended to the outpatient service.

Material and Method: Prescribing data and registered populations between October 1, 2008 and September 30, 2010 were retrieved from the database and analyzed.

Result: Original and generic expenditure rose 8.42 and 8.61% from 2009 to 2010 respectively. Among 228 mandatory items, more original was switched to generic drugs, both in terms of value (6.5 to 7.2%) and in terms of volume (32.5 to 33.8%). Some inpatients, mainly civil servants and self-pay patients, requested the original from the outpatient service where the mandatory substitution was not applied. If the policy were extended through all services, the government would save approximately 306.5 million Baht (US$ 10.1 million) per year. However, the hospital would reduce its profit by 53.1 million Baht (US$ 1.7 million).

Conclusion: After the policy was launched, more original mandatory drugs were switched to generic. To gain more saving, the policy may be expanded to outpatient service, and/or mandatory drug list should be reviewed periodically.

Keywords: Generic substitution, Drug expenditure, Hospital database, Thai teaching hospital